J. Cent. South Univ. (2019) 26: 768−778 DOI: https://doi.org/10.1007/s11771-019-4046-2 Sensitivity analysis of geomechanical parameters affecting a wellbore stability Abolfazl ABDOLLAHIPOUR 1 , Hamid SOLTANIAN 1 , Yaser POURMAZAHERI 1 , Ezzatollah KAZEMZADEH 1 , Mohammad FATEHI-MARJI 2 1. Division of Petroleum Engineering, Faculty of Upstream Petroleum Industry, Research Institute of Petroleum Industry (RIPI), Tehran 14665-37, Iran; 2. Faculty of Mining and Metallurgical Engineering, Yazd University, Yazd 89195-741, Iran © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract: Wellbore stability analysis is a growing concern in oil industries. There are many parameters affecting the stability of a wellbore including geomechanical properties (e.g., elastic modulus, uni-axial compressive strength (UCS) and cohesion) and acting forces (e.g., field stresses and mud pressure). Accurate determination of these parameters is time-consuming, expensive and sometimes even impossible. This work offers a systematic sensitivity analysis to quantify the amount of each parameter’s effect on the stability of a wellbore. Maximum wellbore wall displacement is used as a stability factor to study the stability of a wellbore. A 3D finite difference method with Mohr model is used for the numerical modeling. The numerical model is verified against an analytical solution. A dimensionless sensitivity factor is developed in order to compare the results of various parameters in the sensitivity analysis. The results show a different order of importance of parameters based on rock strength. The most sensitive properties for a weak rock are the maximum horizontal stress, internal friction angle and formation pressure, respectively, while for a strong rock, the most sensitive parameters are the maximum horizontal stress, mud pressure and pore pressure, respectively. The amount of error in wellbore stability analysis inflicted by the error in estimation of each parameter was also derived. Key words: wellbore stability; sensitivity analysis; numerical modeling Cite this article as: Abolfazl ABDOLLAHIPOUR, Hamid SOLTANIAN, Yaser POURMAZAHERI, Ezzatollah KAZEMZADEH, Mohammad FATEHI-MARJI. Sensitivity analysis of geomechanical parameters affecting a wellbore stability [J]. Journal of Central South University, 2019, 26(3): 768–778. DOI: https://doi.org/10.1007/s11771-019- 4046-2. 1 Introduction Wellbore instability is one of the key challenges influencing the drilling and production operations. Problems associated with it are both time-consuming and expensive. Therefore, an accurate prediction of wellbore state is of paramount importance. There are many parameters affecting the behavior of a wellbore both during drilling and production stages including fluids’ viscous behavior, temperature, etc [1–3]. Instability mechanisms may be caused by two mechanisms: mechanical interactions by in-situ stresses [4, 5], formation geomechanical properties [6–8], formation pressure (pore pressure), and physicochemical interactions of drilling fluid and shale formations [9–14]. YAN et al [1] studied the effects of drilling fluid circulation, drilling fluid density, and mud displacement on the stability of a wellbore in high-temperature formations. They showed that fracture pressure and closure pressure both increase with the increase of the borehole temperature. Many studies have focused Received date: 2017-12-21; Accepted date: 2018-02-12 Corresponding author: Ezzatollah KAZEMZADEH, PhD, Associate Professor; Tel/Fax: +98-21-48252591; E-mail: Kazemzadehe@ ripi.ir; ORCID: 0000-0003-2687-4470